Method, Apparatus and Computer Program for Signaling Channel Quality Information in a Network that Employs Relay Nodes

ABSTRACT

A relay node receives from user equipments UE CQI reports which give a CQI value per radio band resource RBR, from which are aggregated across the RBRs and/or aggregated per UE across that UE&#39;s RBR values. The relay node reports an indication of the average to its controlling access node (eNodeB), either explicitly or implicitly (e.g., a gain applied to the CQI of the downlink between the relay and access nodes). The relay node also checks the UEs&#39; buffer status (actual or predicted) and reports either periodically or based on an underflow/overflow occurrence. For periodic reports, each UE buffer experiencing the overrun/underrun is reported.

TECHNICAL FIELD

The exemplary and non-limiting embodiments of this invention relategenerally to wireless communications systems and, more specifically,relate to the communication of channel quality information for channelsin a network that uses relay nodes, and further how that information maybe used for scheduling decisions.

BACKGROUND

The following abbreviations are used in the description below:

-   3GPP third generation partnership project-   CQI channel quality information-   DL downlink-   e-NodeB Node B of an E-UTRAN system-   eNBr relay-enhanced eNB-   E-UTRAN evolved UTRAN-   LTE long term evolution of 3GPP UTRAN (E-UTRAN or 3.9G)-   Node B base station or similar network access node, including    e-NodeB-   RAN radio access network-   RBR radio band resource-   RN relay node-   RS relay station-   QoS Quality of Service-   UE user equipment (e.g., mobile equipment/station)-   UL uplink-   UMTS universal mobile telecommunications system-   UTRAN UMTS terrestrial radio access network

3GPP is standardizing the long-term evolution (LTE) of the UMTSradio-access technology which aims to achieve reduced latency, higheruser data rates, improved system capacity and coverage, and reduced costfor the operator. Future LTEs standard releases (here termed Release 9for brevity) may use relay nodes (RNs), alternatively termed relaystations (RSs), in order to enhance coverage areas in the cell of ane-NodeB. FIG. 1 gives an overview of how such RNs can be used toadvantage: to extend wireless coverage to the interior of a building, toextend coverage beyond the cell edge (cell edge as defined by the radiorange from the e-NodeB), to direct radio signals more particularly to avalley between buildings or to a radio-frequency ‘shadow’ behind abuilding, to extend the cell to other non-contiguous areas such as viamulti-hops/multi-relays, and to provide robust radio signals in anyother ‘coverage holes’ that may be at different areas of the cell. TheRNs can be fixed or mobile, such as mounted to a high-speed train. Insome systems the relay stations may be opportunistically availableUEs/mobile terminals that are not owned by the network itself. Forclarity, a network access node that employs RNs is termed a relayenhanced access node, or in the context of LTE it is termed an e-NBr forbrevity.

Apart from this main goal of coverage extension, introducing relayconcepts in LTE can also be used to aid in the provisioning ofhigh-bit-rate coverage in high shadowing environment, to reduce theaverage radio-transmission power at the UE which extends the UE'sbattery life, to enhance cell capacity and effective throughput (e.g.,by increasing cell-edge capacity and balancing cell load), and toenhance overall performance and deployment cost of the radio accessnetwork RAN.

After being carefully considered in pre-standardization activities likethe Wireless World Initiative WWI/Wireless World Initiative New RadioWINNER system concept, relay systems are achieving the level of maturitythat is needed in ongoing LTE standardization activities. The WINNERconcept seeks to develop a system that is QoS aware and uses intelligentscheduling to meet user demands and physical constraints, in a modelthat is scalable for deployment to any of various spectrum types andbandwidths including spectrum sharing. This scalable deployment givesrise to relay nodes being an important part of the WINNER concept. As anexample of later stages of relay node development, the IEEE 802.16jstandardization adds relays to the IEEE 802.16e standard. This recentdevelopment has increased the pressure to consider relays also in LTEstandardization. Certain wireless network operators have been activelypushing for relay standardization since it is expected that relaysystems will be economically viable due to reduced backhaul and siteacquisition costs. In order to keep LTE competitive it is more thanprobable that relay extensions to LTE are to be studied within 3GPP inthe release 9. Various topics will be studied and relays appear likelyto play an important role in LTE Release 9, and RSs are likely to beincluded in the LTE Release 9 agenda.

There are many specific types of relay systems proposed, from the simple(e.g., amplify/forward implementations, applied in single frequencynetworks such as digital video broadcast for handhelds DVB-H, forexample) to the more complex such as using network coding to improve theoverall performance. A common relay type that is proposed for cellularrelaying is a detect/forward type of relay, where an input signal isdetected and retransmitted using the same procedure as in the originaltransmission. The following discussion assumes the detect/forward typeimplementation for a relay network.

To ensure economic viability in adopting RNs into the LTE network,backward compatibility between Release 8 (standardization ongoing) andRelease 9 will be needed. A reasonable assumption is that full backwardcompatibility is required from the UE perspective, i.e. Release 8 andRelease 9 terminals should work equally well in Release 8 and in Release9 networks. At the network side software and even hardware updatesbetween standard releases may be possible but preferably they should beas small as possible. Hence, from the UE viewpoint the serving networknode should function in exactly the same way as the e-NodeBs of Release8. Due to this requirement, the reduction of functionalities of thee-NodeB when defining and implementing relay nodes will be difficult,and the relay nodes will need to support all of the main e-NodeBfunctions also. Due to this fact it can be assumed that relay nodes arecapable of flexible resource sharing with the e-NodeB that controlsthem.

Assuming no RNs in an LTE (also known as E-UTRAN or 3.9G) cell so thatthe UEs and the e-NodeB communicate directly, the link adaptation andscheduling procedures utilize channel quality information (CQI) reportsfrom the active UEs. An ideal CQI report tells the e-NodeB the qualityof each radio band resource (RBR) that the corresponding UE being servedmeasures. The e-NodeB can utilize this information for optimalscheduling and link adaptation. However, ideal CQI reporting on an RBRbasis is not practical due to the limited number of pilot symbolsavailable and also to the need to control the volume of controlsignaling overhead. The prior art does address several low bandwidth CQIschemes, the most representative ones seen to be offset CQI, thresholdCQI and best-M CQI reporting.

The introduction of RNs can have an impact on the overall architectureof the network as well as the CQI reporting and its usage for schedulingand link adaptation. The scheduling of UEs under control of a RN can bedone by the RN with the help of the controlling e-NodeB (e.g., where theRN is given some authority to schedule radio resources given by thee-NodeB), or solely by the controlling eNBr (where the RN acts as acommunication conduit and all scheduling decisions are by the e-NodeB).

Certain problems arise in the former case. The RN may be doing thescheduling, but the impact of erratic radio channels has to be takeninto account so that the controlling eNBr is able to assign sufficientradio resources for the RN to operate and provide adequate quality ofservice (QoS) to each relayed UE. For instance, a situation may arisewhen a certain relayed UE's buffer in the RN is being overfilled becausethe RN-UE link for that UE is very bad (low CQI) and it is not beingscheduled by the RN, while at the same time the e-NodeB keeps sendingdata for that UE in the eNBr-RN link, which has a sufficiently good linki.e. high CQI. This is a flow control problem with no analogy to thecase where the link is direct between the UE and the e-NodeB and thereare no RNs between them.

The introduction of RNs is a new concept in LTE. Thus, scheduling andassociated CQI reporting has not been considered previously. The casewhere RNs control the scheduling of its own users is similar to thenon-transparent mode defined in WIMAX. However, the issues regarding CQIreporting and scheduling are not resolved since those are different inLTE.

What is needed in the art is an approach to optimize scheduling of UEsunder control of a RN for various actual channel conditions that existbetween the RN and the UEs under its control, preferably in a mannerthat is consistent with LTE.

SUMMARY

In accordance with one aspect of the invention is a method that includesreceiving from a plurality of user equipments indications of channelquality experienced by the user equipments, then aggregating thereceived indications into a compound signal quality metric. Thereafter,the method continues with sending an indication of the compound signalquality metric to an access node controlling a cell in which the userequipments operate. In a particular embodiment, the format and signalingprocedure to indicate this metric information can be layer 1 L1 orhigher (e.g., L2 Medium Access Control MAC layer or L3 Radio ResourceControl RRC layer).

In accordance with another aspect of the invention is an apparatus thatincludes a receiver, a processor and a transmitter. The receiver isconfigured to receive from a plurality of user equipments indications ofchannel quality experienced by the user equipments. The processor isconfigured to aggregate the received indications into a compound signalquality metric. The transmitter is configured to send an indication ofthe compound signal quality metric to an access node controlling a cellin which the user equipments operate.

In accordance with another aspect of the invention is a computerreadable memory embodying a program of machine-readable instructionsexecutable by a digital data processor to perform actions directedtoward sending quality indications. In this embodiment the actionsinclude, responsive to receiving from a plurality of user equipmentsindications of channel quality experienced by the user equipments, andaggregating the received indications into a compound signal qualitymetric. Further, the actions include sending an indication of thecompound signal quality metric to an access node controlling a cell inwhich the user equipments operate.

In accordance with another aspect of the invention is an apparatus thatincludes receiving means for receiving from a plurality of userequipments indications of channel quality experienced by the userequipments, processing means for aggregating the received indicationsinto a compound signal quality metric, and transmit means for sending anindication of the compound signal quality metric to an access node thatcontrols a cell in which the user equipments operate. In a particularembodiment the receiving means is a wireless receiver, the processingmeans is a digital data processor, and the transmit means is a wirelesstransmitter, and the apparatus is a relay node in a LTE network cell.

In accordance with another aspect of the invention is a method thatincludes allocating in a first instance radio resources to a relay nodefor use by user equipments under control of the relay node, receivingfrom the relay node a compound signal quality metric that aggregateschannel quality on links between the user equipments and the relay node,deciding a new allocation of radio resources based at least in part onthe compound channel quality metric, and allocating in a second instancethe new allocation of radio resources to the relay node. In a particularembodiment there is also received an indication of buffer occupancy ofthe relay node, and the new allocation is decided so as to manage flowcontrol from the user equipments as a function of the compound signalquality metric and the received buffer occupancy.

In accordance with another aspect of the invention is an apparatus thatincludes a transmitter, a processor and a receiver. The transmitter isconfigured to send to a relay node in a first instance radio resourcesfor use by user equipments under control of the relay node. The receiveris configured to receive from the relay node a compound signal qualitymetric that aggregates channel quality experienced on links between theuser equipments and the relay node. The processor is configured todecide a new allocation of radio resources based at least in part on thereceived compound channel quality metric. And the transmitter is furtherto send to the relay node in a second instance the new allocation ofradio resources.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of these teachings are made more evidentin the following Detailed Description, when read in conjunction with theattached Drawing Figures.

FIG. 1 is a schematic diagram showing a relay network with a controllingaccess node and various relay nodes serving to enhance coverage formobile terminals in various scenarios, a context which is relevant tothese teachings.

FIG. 2 shows a simplified block diagram of various electronic devicesthat are suitable for use in practicing the exemplary embodiments ofthis invention.

FIG. 3 illustrates channel quality indicators reported by various UEsunder control of a relay node for various radio band resources, arrangedin a table, and resulting averages calculated by the relay node forreporting to the access node/e-NodeB according to certain embodiments ofthe invention.

FIG. 4 is a process flow diagram illustrating process steps according toa particular embodiment of the invention.

DETAILED DESCRIPTION

These teachings focus primarily on the case where the RNs take the mainresponsibility for scheduling their users. In this case, it may not beneeded for the e-NodeB to be aware of the CQI between RN and individualrelayed UEs, though for reasons noted above it is important from a flowcontrol perspective that the e-NodeB not be wholly unaware of thequality of the UE-RN link. Embodiments of this invention provide asolution to such a flow control problem. While specific examples arepresented in the particular context of LTE, the invention is not limitedonly to LTE but may be employed in any wireless access network thatemploys relay nodes under control of a controlling access node.

For the description below it is assumed that at maximum two hops areallowed per communication (between UE and e-NodeB or between UE and RNand e-NodeB), and the relay nodes are arranged in a tree topology (noconnections between relay nodes). Note that this second assumptionexcludes two instances shown in FIG. 1. The invention is not limited byeither of these two assumptions, but they are noted as constraining thespecific examples given rather than the breadth of these teachings.Embodiments of the invention can be used with other network topologies,and/or across more than two-hop links.

Embodiments of this invention relate to integrating information at theRN, and sending that integrated information to the e-NodeB which canthen be used for UE scheduling and for controlling the flow of DL datato the UEs in a relay enhanced LTE network. The integrated informationis a quality metric indicative of the link between the RN and the UEsunder its control, but the quality metric is compound rather thanreflective of an individual link. The compound metric may be, forexample, averaged over multiple UEs or over multiple RBRs in order toreduce signaling overhead on the link between the RN and the eNBr, ascompared to forwarding all the CQI values that the U Es report to theRN. This compound information can still be used to enhance datatransmission on the link going between the eNB and the RN to avoidbuffer over/under run as noted above, and also for the eNBr to assignsuitable resources for the links between the RN and the UEs.

As a preliminary matter before exploring details of variousimplementations, reference is made to FIG. 2 for illustrating asimplified block diagram of various electronic devices that are suitablefor use in practicing the exemplary embodiments of this invention. InFIG. 2 a wireless network 9 is adapted for communication between a UE 10and a Node B 12 (e.g., a wireless access node, such as a base station orparticularly an eNBr for a LTE system). The network 9 may include agateway GW/serving mobility entity MME/radio network controller RNC 14or other radio controller function known by various terms in differentwireless communication systems. The UE 10 includes a data processor (DP)10A, a memory (MEM) 10B that stores a program (PROG) 10C, and a suitableradio frequency (RF) transceiver 10D coupled to one or more antennas 10E(one shown) for bidirectional wireless communications over one or morewireless links 20 with the eNBr 12.

The terms “connected,” “coupled,” or any variant thereof, mean anyconnection or coupling, either direct or indirect, between two or moreelements, and may encompass the presence of one or more intermediateelements between two elements that are “connected” or “coupled”together. The coupling or connection between the elements can bephysical, logical, or a combination thereof. As employed herein twoelements may be considered to be “connected” or “coupled” together bythe use of one or more wires, cables and printed electrical connections,as well as by the use of electromagnetic energy, such as electromagneticenergy having wavelengths in the radio frequency region, the microwaveregion and the optical (both visible and invisible) region, asnon-limiting examples.

The eNBr 12 also includes a DP 12A, a MEM 12B, that stores a PROG 12C,and a suitable RF transceiver 12D coupled to one or more antennas 12E.The eNBr 12 may be coupled via a data path 30 (e.g., lub or S1interface) to the serving or other GW/MME/RNC 14. The GW/MME/RNC 14includes a DP 14A, a MEM 14B that stores a FROG 14C, and a suitablemodem and/or transceiver (not shown) for communication with the Node B12 over the lub link 30. Also shown as part of the MEM 12B is aplurality of buffers 12G for storing data and information to be sentover one of the wireless links 20, 20B. These buffers 12G are detailedmore particularly below.

Also within the eNBr 12 is a scheduler 12F that schedules the variousUEs under its control for the various UL and DL radio resources (RBRsand transmission time resources). Once scheduled, the e-NodeB sendsmessages to the UEs with the scheduling grants (typically multiplexinggrants for multiple UEs in one message). These grants are sent overparticular channels such as the Physical Downlink Control Channel(PDCCH) in LTE. Generally, an e-NodeB of an LTE system is fairlyautonomous in its scheduling and need not coordinate with the GW/MME 14excepting during handover of one of its UEs to another Node B/e-NodeB orfor the purpose of other higher layer reconfiguration signaling.

The network also employs a RN 16, shown also as having a DP 16A and aMEM 16B that stores a PROG 16C, and using a transceiver (transmitter andreceiver) 16D for communications via at least one antenna 16E over afirst link 20A with the UE 10 (as well as other UEs under the RN'scontrol) and over a second link 20B with the eNBr 12 that is controllingthe cell. In the embodiments detailed below, the direct link 20 betweenthe eNBr 12 and the UE 10 is not in active use but insteadcommunications are routed through the RN 16 via the first and Secondlinks 20A, 20B. The RN 16 may also have a scheduler 16F for allocatingradio resources (RBRs) to the UEs under its control, for the caseconsidered here where the eNBr 12 grants the RN 16 a block of radioresources for use in its area of the cell for allocating to those UEsunder the RN's control.

At least one of the PROGs 10C, 12C and 16C is assumed to include programinstructions that, when executed by the associated DP, enable theelectronic device to operate in accordance with the exemplaryembodiments of this invention, as detailed above. Inherent in the DPs10A, 12A, and 16A is a clock to enable synchronism among the variousapparatus for transmissions and receptions within the appropriate timeintervals and subframes required, as the scheduling grants and thegranted resources/subframes are time dependent. The transceivers 10D,12D, 16D include both transmitter and receiver, and inherent in each isa modulator/demodulator commonly known as a modem. The DPs 12A, 14A and16A also are assumed to each include a modem to facilitate communicationover the (hardwire) link 30 between the eNBr 12 and the GW 14 and overthe various wireless links 20, 20A, 20B shown between the particularelectronic apparatuses.

The PROGs 10C, 12C, 16C may be embodied in software, firmware and/orhardware, as is appropriate. In general, the exemplary embodiments ofthis invention may be implemented by computer software stored in the MEM16B and executable by the DP 16A of the RN 16 and similar for the otherMEM 12B and DP 12A of the eNBr 12, or by hardware, or by a combinationof software and/or firmware and hardware in any or all of the devicesshown.

In general, the various embodiments of the UE 10 can include, but arenot limited to, mobile stations, cellular telephones, personal digitalassistants (PDAs) having wireless communication capabilities, portablecomputers having wireless communication capabilities, image capturedevices such as digital cameras having wireless communicationcapabilities, gaming devices having wireless communication capabilities,music storage and playback appliances having wireless communicationcapabilities, Internet appliances permitting wireless Internet accessand browsing, as well as portable units or terminals that incorporatecombinations of such functions. Embodiments of the RN may be a UE or maybe a fixed or mobile access node under control of the controlling eNBrthat is controlling in the cell.

The MEMs 10B, 12B and 16B may be of any type suitable to the localtechnical environment and may be implemented using any suitable datastorage technology, such as semiconductor-based memory devices, magneticmemory devices and systems, optical memory devices and systems, fixedmemory and removable memory. The DPs 10A, 12A and 16A may be of any typesuitable to the local technical environment, and may include one or moreof general purpose computers, special purpose computers,microprocessors, digital signal processors (DSPs) and processors basedon a multi-core processor architecture, as non-limiting examples.

Now are described the particular embodiments of the invention in detail.The end result is that scheduling and controlling the flow of DL data isintegrated in a relay enhanced network such as an LTE network. Accordingto an embodiment, a plurality of UEs under control of a relay node sendto the RN the CQI measurements for RBRs allocated to the system/cell(not only those RBRs in use and assigned to the respective UEs). The RNreceives these messages, and aggregates information from those messagesinto a compound signal quality metric. The RN then sends the compoundsignal quality metric to the eNBr. The aggregating may be over multipleUEs, or it may be for multiple RBRs allocated to the same UE, or it maybe over some combination of a plurality of RBRs and UEs including allUEs and all RBRs. The latter may be practical where the RN has controlover only a fairly limited geographic area and/or very limited radioresources. The compounding is in one embodiment averaging signal qualityof the received CQI measurements.

It is clear then that the compounded signal quality metric can besignaled with fewer bits than the individual RBR CQI values that arereported by the UEs 10 to the RN 16, and so embodiments of the inventionreduce signaling overhead on the link 208 between the RN 16 and the eNBr14. This compound information can still be used to enhance datatransmission on the link 20B between the eNBr 12 and the RN 16 to avoidbuffer over/under run and also for the eNBr 12 to assign suitableresources for the links 20A between the RN and the UE.

The RN 16 has the CQI information available for all of its users/UEs 10and it can summarize this CQI information and send it to the eNBr 12 inone of at least two ways as noted above, denoted here as the compoundsignal quality metrics:

CQI_AVG_RBR: The CQI for each RBR is averaged over all the UEs.

CQI_AVG_UE: The CQI for each UE is averaged over all the RBRs.

This is shown diagrammatically at FIG. 3, which is a tabular form of theCQI information arranged by UEs (UE₁, UE₂, . . . UE_(N)) along rows andarranged by RBRs along columns. Within the table, each of the entriesCQI is the CQI value reported by the UE 10 of that row for the RBR forthat column. RBR is a frequency band corresponding to one or morephysical resource blocks as defined in the LTE standard. The lowermostrow below the table of CQI values (with entries C1 _(c), C2 _(c), C3_(G) represent the RBR averaged quality, the CQI-AVG-RBR for the i^(th)RBR column, where there are M RBRs and i is an integer index of the RBRsfrom 1 thorough M. Similarly, the rightmost column of FIG. 3 outside thetable of CQI values (with entries C1 _(R), C2 _(R), C3 _(R), . . .CN_(R)) represent the UE averaged quality, the CQI-AVG-UE for the j^(th)UE column, where there are N UEs and j is an integer index of the UEs 10under control of the RN 16 from 1 thorough N. Note that compressed CQIreporting schemes proposed for LTE Release 8 (e.g., threshold based,Best-M, etc.) can still be used along with the aggregating mechanismsproposed here. Such compression schemes are known in the art and notdetailed here further. When the values reported by the UEs are thecompressed CQI values, it is straightforward for the RN 16 to averageover the reported Best-m (or other compression) CQIs which are likely tobe used for scheduling to achieve the above CQI-AVG-RBR and/orCQI-AVG-CQI.

The CQI_AVG_RBR metric gives an average indication on which RBRs are themost suitable for the transmission between the RN 16 and the servedusers/UEs 10. As such, the eNBr 12 can use this information to decidewhich RBRs can be allocated to RN 16 for the next scheduling period onthe RN-UE link 20A. The RN 16 can pass the CQI_AVG_RBR informationexplicitly (we name this case CQI_Averaged) or it can pass it implicitlyby using it as a weighting factor when it reports the CQI of the eNBr-RNlink 20B (CQ/Weighted). In the latter, the weighting is done by mappingthe CQI_AVG_RBR into a gain factor. That is, if UEs 10 being served bythe RN 16 are experiencing bad channel condition on the average, the CQIof the eNBr-RN link 20B will be reduced by the gain factor while whenthey are experiencing very good channel conditions, it will be increasedby the gain factor. Note that in an embodiment CQI_Weighted andCQI_Averaged can be used together, where the RN reports both to the RNbut at different reporting rates.

Note that the actual scheduling and allocation of the RBRs can still bedone by the RN 16 individually for each UE 10, but with the help ofCQI_AVG_RBR the eNBr 12 can better decide which pool/group of RBRs toassign to the RN 16 for the RN-UE links 20A and which other RBRs to use(e.g. for direct transmission) from the eNBr 12 to other, directlyserved UEs. Furthermore, if there are RNs 16 in close vicinity to eachother, it may be beneficial to allocate at least partly non-overlappingRBR pools to both RNs 16 in order to avoid or reduce interferencebetween the two. This is particularly advantageous, if the RNs 16 serveoverlapping areas, this may well happen if RN locations are not strictlyplanned, or if one or more of the RNs are mobile (e.g., on a high-speedtrain). The described CQI_AVG_RBR then allows the eNBr 12 to assign theRBRs optimally to the RNs 16 (i.e. each gets the RBRs that will giveoptimum performance for the assigned UEs 10).

On the other hand, CQI_AVG_UE tells which UEs 10 are experiencing thebest radio conditions in the access links on the average. Using thisinformation, the eNBr 12 decides which UEs' data and how much data foreach UE to send on the eNBr-RN link 20B and this will help in mitigatingthe flow control problem described in the background section above. Thisis because the eNBr 12 is giving priority to the UEs 10 experiencinggood radio conditions and as such both over-buffering and bufferunder-run in the RN 16 is prevented.

In an embodiment, both the CQI-AVG-UE and the CQI-AVG-RBR are used, butare sent at different times. The RN 16 forwards both reportsperiodically, but not necessarily with the same period. The actualreporting periods are parameters to be determined through optimizationprocedures that depend on the operating network. The flow controlinformation (i.e. CQI_AVG_UE) can also be reported on an event-basedfashion (for example, when the averaged CQIs of the UEs 10 are showingtoo much difference, as reporting when they are very similar will notprovide any useful information for the eNBr 12.)

The deployment of RNs 16 reduces the dynamic of CQI range for relayedusers and therefore a simple averaging may be sufficient for theCQI_AVG_UE to meet the needs of the eNBr 12. However, since the UE 10 isgoing to be scheduled in the RBRs that are experiencing good quality,the CQI_AVG_UE calculation can take this into consideration by weightingthe RBRs that are experiencing good conditions more than the ones thatare experiencing bad conditions. In this way a better estimation of theexperienced channel quality in the RBRs where the UE 10 is actuallyscheduled can be achieved.

It is possible to perform flow control based on the CQI_AVG_UE reportsas described above, but flow control can be performed more explicitlyvia buffer status reporting. Within the RN 16 there is a buffer 16G foreach of the UEs 10 under its control. It is the status of these buffers16G to which the following refers. For this explicit buffer statusreporting, the RN 16 reports to the eNBr 12 the buffer status of its UEs10 in one of at least two fashions, or their combination, termed hereinPeriodic and Early Detection.

For periodic reporting, a semi dynamic variable,RN_buffer_status_reporting_period, is used. The RN 16 reportsperiodically every RN_buffer_status_reporting_period its buffer statuscorresponding to each of the U Es that it is serving. The eNBr 12 willinform the RN 16 of the reporting period according to a particularembodiment.

For early detection reporting, two semi dynamic variables are used,RN_buffer_overload_limit and RN_buffer_underload_limit. In an embodimentthese are each percentage values, and are used as threshold by which togenerate a report to the eNBr 12. When the buffer of a certain UE 10 atthe RN 16 becomes higher than the RN_buffer_overload_limit or when itbecomes lower than RN_buffer_underload_limit, the RN reports a bufferstatus report to the eNBr 12 with the information regarding this. Notethat the RN_buffer_underload_limit is effective only once after theRN_buffer_overload_limit has been reported. These reports can be doneinstantaneously, i.e. when the limits are reached, or optionally, avariable RN_buffer_overload_underload_reporting_period, can be usedwhere the RN 16 reports periodically the buffers of all of the UEs thathave passed these limits.

The eNBr 12 will then be able to use these reports during scheduling. Ifperiodic reporting is used, the operation is similar to the CQI_AVG_UEbased flow control, i.e. UEs with the largest buffer occupancy in the RN16 can be either given lower priority, or not even scheduled at all fora given period. On the other hand, with early detection, the eNBr 12could give low priority to the UEs 10, or even pause the scheduling whenthey report RN_buffer_overload_limit and raise their priority (or resumetheir scheduling in case the decision was to pause their scheduling)when they report RN_buffer_underload_limit.

The various techniques detailed above can be used in combination. Forexample, the network 9 can use a combination of the buffer based and theCQI_AVG_UE based flow control for an efficient and robust operation. Forexample, the network 9 can use the RN early-detection buffer-statusreporting of individual UEs combined with the averaged CQI reporting forflow control and resource re-assignment between the controlling eNBr 12and its RN 16.

Furthermore, the CQI_AVG_UE can be used to make a prediction when thebuffer may under-run or over-run. The RN 16 can then report at apredetermined time before the buffer under-run instead of reporting at afixed buffer size RN_buffer_underload_limit. The advantage of thisapproach is that then the eNBr 12 always has the same time to reactuntil the buffer actually gets empty (or overfull), while using a fixedvalue of RN_buffer_underload_limit would mean that UEs 10 whichexperience a good channel condition will deplete the buffer quicklywhile the UEs 10 with a poor channel will take much longer to depletethe same amount of data. Therefore, taking the CQI_AVG_UE into accountcan help to better select for which UEs 10 to forward data to the RN 16,namely for those UEs 10 whose buffer threatens to be depleted at theearliest. Using the achieved data rates in the past can also be used forthis purpose, but CQI gives a better estimate for the future data rateswhich are more relevant to anticipating buffer over-run and under-run.

Note that the combination of CQI_AVG_UE and RN_buffer_underload_limitcan be done in the RN 16, then the compound information taking both intoaccount can be signaled to the eNBr 12. Alternatively, both values couldbe signaled individually to the eNBr 12 and the eNBr 12 takes them bothinto account. The former approach saves some signaling overhead on thesecond link 20B while the latter approach gives more completeinformation to the eNBr 12.

In the exemplary embodiment described above, the buffer status and thecompound CQI information was combined into a prediction of the time whenthe buffer would under run or over run. Note however, that variousvariants of this approach are possible by combining buffer status andCQI in another way and still convey some information about the bufferstatus, even if it is not exactly the time expected for bufferdepletion. For example, some maximum or minimum data rates can beconsidered during calculation rather than fully obeying the compound CQIinformation. Also further information and parameters can be taken intoaccount, e.g. the priority of a user or a service, because high prioritydata/users may be scheduled with higher priority and therefore theassociated buffers are likely to under run more early.

Further more, it is not only possible to aggregate CQI values and bufferstatus for individual users, but also for user classes e.g. userssharing the same or similar priority class. This is motivated by thefollowing arguing: the RN will have to take care that data are scheduledin a fair way for users within a certain priority class, but thescheduling priority and consequently the achievable data rates may varygreatly for users of different priority classes. Therefore it may besufficient to report only for a single user of a priority class ofreport a value that is aggregated i.e. compound e.g. averaged forseveral or all users of a specific priority class. In this way thesignaling overhead can be further reduced, without substantial loss ofuseful knowledge at the eNodeB.

For the case where ideal CQI forwarding is used (all CQI values reportedfrom the UEs are forwarded through the RN to the eNBr), the RN 16 willneed to send m×n (considering m RBRs are reported per UE, and there aren UEs) information elements. With the CQI_Weighted implementation, thisis reduced to zero because the RN 16 doesn't send any extra informationexplicitly. Even without using CQI_Weighted, the amount of informationelements to be sent to the eNBr 16 is reduced to m for the case whereCQI_AVG_UE is used, or to n for the case where CQI_AVG_RBR is used, orto m+n for the case where both are used. In all cases this is lesssignaling overhead than relaying the m×n CQI information elementsreported by the UEs 10.

It is noted that CQI_Weighted reporting may be appropriate even thoughthe channel qualities of the relay link 20B and the access links 20A canbe quite different, e.g. because the relay node is typically fixed andtherefore the channel quality for the eNBr-RN link 20B is more or lessstable or slowly time-varying varying only. Note however, that also theinverse may happen e.g. for relays mounted on trains or other vehicles,there the channel quality for the eNBr-RN link 20B can vary quicklywhile the channel between relay and terminal is rather stable, because avoyager typically doesn't move quickly within the vehicle. Therefore thereporting rates on the two links may be substantially different. Alsothe times above which the data are accumulated or averaged may vary aswell. If the channel quality of the link between terminal and RN ischanging so quickly that reports cannot be done in time to the eNodeB,then it may be better not to report instantaneous values but ratheraveraged values over some time and also averaged over possible RBRs. Itis possible to get more reliable information by averaging over thequality of individual RBRs in time and frequency.

The flow control mechanisms described here generally do not require anyimplementation change at the UEs. Also, the CQI-based scheduling that isbased on the weighted CQI does not require any changes at the eNBr 12 ascompared with a relay enhanced system with no relay link CQI-basedscheduling, because the eNBr 12 in that case treats the weighted CQI asthe CQI of the backhaul link (the DL between the RN 16 and the UE 10).The various compressed CQI reporting schemes proposed for LTE Release 8(threshold based, Best-M, etc.) can still be used for the RN-UE link,thus further reducing the signalling on the both RN-eNB and UE-RN links.

Both flow control mechanisms described avoid the need for forwarding theCQI of each relayed user to the eNBr 12 via the RN 16, and hence greatlyreduce the CQ!-related signaling overhead. The buffer based flow controlis seen to be more accurate in tracking indirectly the CQI of the accesslinks 20A as compared with the CQI_AVG_UE based flow control, but itrequires somewhat more control signaling.

Scheduling based on the weighted CQI reporting does not have anyoverhead, because one CQI report is still sent, but if the RN 16 isserving a very small number of users, the averaging and weighting mightresult in suboptimal scheduling as one UE 10 that is in a very badcondition can drag the performance of another one experiencing excellentchannel conditions. Thus, the weighted CQI option becomes moreattractive when the number of users served by the RN 16 is considerable.A more advanced flow control algorithm can be employed that takes intoaccount this fact by switching from CQI_averaged to CQI_weighted (andvice versa) scheduling depending on the number of relayed users, such asusing a ratio of variance between best and worst CQI and number of UEsfor determining whether to use one flow control metric or the other.

If there are more than one RNs 16 in a cell and if each is serving aconsiderable number of UEs, the weighted CQI can enable fasterscheduling as the users can be grouped easily into sets of prioritygroups depending on the weighted CQI of the backhaul link.

Some of the major points detailed above are summarized at FIG. 4. Atblock 402 the RN 16 receives from the UEs 10 under its control the CQIreports, which give a CQI value per RBR. These CQI reports can be basedon any of the compressed CQI reporting schemes proposed for LTE Release8 (threshold based, Best-M, etc.). At block 404 both averages arecalculated, one from the aggregated RBR values across all of the UEsreporting for that RBR, and the other averaged per UE across all RBRsreported by the respective UE 10. As above, different implementationsuse either or both of these averages. At block 406 the RN 16 reports anindication of the average to the eNBr 12, which may be an explicitaverage sent in the message or it may be implicit such as a gain appliedto the CQI of the link 20B between the RN 16 and the eNBr 12 that the RNreports to the eNBr 12. At block 408 the buffer status for each of theUE-specific buffers in the RN 16 is monitored. For periodic reports,overruns and underruns are reported periodically for each UE bufferexperiencing the overrun/underrun (compare buffer state to thethresholds, or predict it based on actual or anticipated rate). Forevent-based reports, the overrun/underrun determination will cause theRN 16 to send the report at block 408.

For the aspects of this invention related to network, embodiments ofthis invention may be implemented by computer software executable by adata processor of the RN 16, such as the processor 16A shown, or byhardware, or by a combination of software and hardware. For the aspectsof this invention related to eNBr 12, embodiments of this invention maybe implemented by computer software executable by a data processor ofthe eNBr 12, such as the processor 12A shown, or by hardware, or by acombination of software and hardware. Further in this regard it shouldbe noted that the various logical step descriptions above may representprogram steps, or interconnected logic circuits, blocks and functions,or a combination of program steps and logic circuits, blocks andfunctions.

In general, the various embodiments may be implemented in hardware orspecial purpose circuits, software (computer readable instructionsembodied on a computer readable medium), logic or any combinationthereof. For example, some aspects may be implemented in hardware, whileother aspects may be implemented in firmware or software which may beexecuted by a controller, microprocessor or other computing device,although the invention is not limited thereto. While various aspects ofthe invention may, be illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it is wellunderstood that these blocks, apparatus, systems, techniques or methodsdescribed herein may be implemented in, as non-limiting examples,hardware, software, firmware, special purpose circuits or logic, generalpurpose hardware or controller or other computing devices, or somecombination thereof.

Embodiments of the inventions may be practiced in various componentssuch as integrated circuit modules. The design of integrated circuits isby and large a highly automated process. Complex and powerful softwaretools are available for converting a logic level design into asemiconductor circuit design ready to be etched and formed on asemiconductor substrate.

Programs, such as those provided by Synopsys, Inc. of Mountain View,California and Cadence Design, of San Jose, Calif. automatically routeconductors and locate components on a semiconductor chip using wellestablished rules of design as well as libraries of pre-stored designmodules. Once the design for a semiconductor circuit has been completed,the resultant design, in a standardized electronic format (e.g., Opus,GDSII, or the like) may be transmitted to a semiconductor fabricationfacility or “fab” for fabrication.

Various modifications and adaptations may become apparent to thoseskilled in the relevant arts in view of the foregoing description, whenread in conjunction with the accompanying drawings. However, any and allmodifications of the teachings of this invention will still fall withinthe scope of the non-limiting embodiments of this invention. Forexample, the channel quality experiences on the links between the userequipments described above in detail assume that communications are doneonly on the radio resources allocated by the relay node, but it mayobtain estimates on other resources also. For example, the relay nodecould send dedicated pilots on a fraction of these resources and theuser equipments could use these pilots for estimations. There arealready ways known in the art to distinguish pilot transmissions fromdifferent eNBs (or relay nodes) such as by using different pilots. Thistechnique is sometimes used on different sectors of the same site thathave some overlap.

Although described in the context of particular embodiments, it will beapparent to those skilled in the art that a number of modifications andvarious changes to these teachings may occur. Thus, while the inventionhas been particularly shown and described with respect to one or moreembodiments thereof, it will be understood by those skilled in the artthat certain modifications or changes may be made therein withoutdeparting from the scope of the invention as set forth above, or fromthe scope of the ensuing claims.

1. A method comprising: Receiving by an apparatus which comprises arelay node, from a plurality of user equipments, indications of channelquality experienced by the user equipments; aggregating by the apparatusthe received indications into a compound signal quality metric;monitoring by the apparatus a buffer status of an apparatus buffer whichcomprises individual buffers for each of the plurality of userequipments; and sending by the apparatus a combination of an indicationof the compound signal quality metric and a further indication of thebuffer status to an access node controlling a cell in which the userequipments operate.
 2. The method of claim 1, further comprising priorto the receiving: receiving at the apparatus a grant from the accessnode of radio band resources that are available for allocation to theuser equipments; and allocating by the relay node to the user equipmentsat least some of the radio band resources; wherein the indications arereceived at the relay node and are specific for a radio band resourceallocated to the respective user equipment.
 3. The method of claim 1wherein received indications from each one of the plurality of userequipments are a plurality of channel quality indications for uniqueones of a plurality of radio band resources.
 4. The method of claim 3,wherein aggregating comprises averaging all of the channel qualityindications that are received for the plurality of radio band resourcesfrom a single one of the user equipments, and the compound signalquality metric is specific to the single one of the user equipments. 5.The method of claim 3, wherein aggregating comprises averaging thechannel quality indications that are received from multiple ones of theuser equipments for a single one of the plurality of radio bandresources. 6-9. (canceled)
 10. The method of claim 1, wherein for afirst instance aggregating comprises averaging all of the channelquality indications that are received by the apparatus from a single oneof the user equipments; and for a second later instance aggregatingcomprises averaging all of the channel quality indications that arereceived by the apparatus from multiple ones of the user equipments fora single radio band resource, wherein sending comprises sending anindication of the respective compound signal quality metric by theapparatus to the access node at different times.
 11. The method of claim1, wherein the indication of the compound signal quality metric is thecompound signal quality metric itself.
 12. The method of claim 1,wherein the indication of the compound signal quality metric comprises again applied to a downlink channel quality parameter that is measured bythe apparatus that receives the indications of channel qualityexperienced by the user equipments.
 13. An apparatus comprising: areceiver configured to receive, from a plurality of user equipments,indications of channel quality experienced by the user equipments; aprocessor configured to aggregate the received indications into acompound signal quality metric and to monitor a buffer status of anapparatus buffer which comprises individual buffers for each of theplurality of user equipments; and a transmitter configured to send acombination of an indication of the compound signal quality metric and afurther indication of the buffer status to an access node controlling acell in which the user equipments operate, wherein the apparatuscomprises a relay node.
 14. The apparatus of claim 13, wherein: thereceiver is configured to receive a grant from the access node of radioband resources that are available for allocation to the user equipments;and the processor is configured to allocate to the user equipments atleast some of the radio band resources; wherein the received indicationsare specific for a radio band resource allocated to the respective userequipment.
 15. The apparatus of claim 13, wherein received indicationsfrom each one of the plurality of user equipments are a plurality ofchannel quality indications for unique ones of a plurality of radio bandresources.
 16. The apparatus of claim 15, wherein the processor isconfigured to aggregate by averaging all of the channel qualityindications that are received for the plurality of radio band resourcesfrom a single one of the user equipments, and the compound signalquality metric is specific to the single one of the user equipments. 17.The apparatus of claim 15, wherein the processor is configured toaggregate by averaging the channel quality indications that are receivedfrom multiple ones of the user equipments for a single one of theplurality of radio band resources. 18-21. (canceled)
 22. The apparatusof claim 13, wherein for a first instance the processor aggregates byaveraging all of the channel quality indications that are received froma single one of the user equipments; and for a second later instance theprocessor aggregates by averaging all of the channel quality indicationsthat are received from multiple ones of the user equipments for a singleradio band resource, wherein the transmitter is configured to send anindication of the respective compound signal quality metric to theaccess node at different times.
 23. The apparatus of claim 13, whereinthe indication of the compound signal quality metric is the compoundsignal quality metric itself.
 24. The apparatus of claim 13, wherein theindication of the compound signal quality metric comprises a gainapplied to a downlink channel quality parameter that the apparatusmeasures.
 25. A computer readable memory embodying a program ofmachine-readable instructions executable by a digital data processor toperform actions directed toward sending quality indications, the actionscomprising: receiving by an apparatus which comprises a relay node, froma plurality of user equipments, indications of channel qualityexperienced by the user equipments; aggregating by the apparatus thereceived indications into a compound signal quality metric; monitoringby the apparatus a buffer status of an apparatus buffer which comprisesindividual buffers for each of the plurality of user equipments; andsending by the apparatus a combination of an indication of the compoundsignal quality metric and a further indication of the buffer status toan access node controlling a cell in which the user equipments operate.26. The computer readable memory of claim 25, wherein each receivedindications from each one of the plurality of user equipments are aplurality of channel quality indications for unique ones of a pluralityof radio band resources, and wherein aggregating comprises at least oneof: aggregating all of the channel quality indications that are receivedfor the plurality of radio band resources from a single one of the userequipments, and the compound signal quality metric is specific to thesingle one of the user equipments; or aggregating the channel qualityindications that are received from multiple ones of the user equipmentsfor a single one of the plurality of radio band resources. 27-30.(canceled)
 31. The computer readable memory of claim 25, wherein theindication of the compound signal quality metric comprises a gainapplied to a downlink channel quality parameter measured by a relay nodethat receives the indications of channel quality experienced by the userequipments.
 32. An apparatus comprising: receiving means for receivingfrom a plurality of user equipments indications of channel qualityexperienced by the user equipments; processing means for aggregating thereceived indications into a compound signal quality metric and formonitoring a buffer status of an apparatus buffer which comprisesindividual buffers for each of the plurality of user equipments; andtransmit means for sending a combination of an indication of thecompound signal quality metric and a further indication of the bufferstatus to an access node that controls a cell in which the userequipments operate, wherein the apparatus comprises a relay node. 33-35.(canceled)
 36. The method of claim 1, wherein the further indication ofthe buffer status comprises a buffer overload or a buffer underloadstate determined individually for one or more of the plurality of userequipments.
 37. The method of claim 36, wherein the buffer overload orthe buffer underload state determined individually for one or more ofthe plurality of user equipments are predicted based on the compoundsignal quality metric.
 38. The method of claim 36, wherein the bufferunderload or the buffer overload is a percentage value.
 39. Theapparatus of claim 13, wherein the further indication of the bufferstatus comprises a buffer overload or a buffer underload statedetermined individually for one or more of the plurality of userequipments.
 40. The apparatus of claim 39, wherein the buffer overloador the buffer underload state determined individually for one or more ofthe plurality of user equipments are predicted based on the compoundsignal quality metric.
 41. The apparatus of claim 39, wherein the bufferunderload or the buffer overload is a percentage value.
 42. The computerreadable memory of claim 25, wherein the further indication of thebuffer status comprises a buffer overload or a buffer underload statedetermined individually for one or more of the plurality of userequipments.
 43. The computer readable memory of claim 42, wherein thebuffer overload or the buffer underload state determined individuallyfor one or more of the plurality of user equipments are predicted basedon the compound signal quality metric.
 44. The computer readable memoryof claim 42, wherein the buffer underload or the buffer overload is apercentage value.
 45. The method of claim 33, wherein the furtherindication of the buffer status comprises a buffer overload or a bufferunderload state determined individually for one or more of the pluralityof user equipments.
 46. A method comprising: allocating by an apparatusin a first instance radio resources to a relay node for allocating bythe relay node to user equipments for use by the user equipments undercontrol of the relay node; sending by the apparatus to the relay node agrant of radio band resources that are available for allocation to theuser equipments; receiving by the apparatus from the relay node acombination of a compound signal quality metric that aggregates channelquality experienced on links between the user equipments and the relaynode using radio band resources from the grant allocated tocorresponding user equipments, and an indication of the buffer status ofa relay node buffer which comprises individual buffers for each of theplurality of user equipments, wherein the further indication of thebuffer status comprises a buffer overload or a buffer underload statedetermined individually for one or more of the plurality of userequipments by prediction based on the compound signal quality metric;deciding by the apparatus a new allocation of radio resources based atleast in part on the compound channel quality metric and on theindication of the buffer status; and allocating by the apparatus in asecond instance the new allocation of radio resources to the relay node.47. An apparatus comprising: a data processor configured to allocate ina first instance radio resources to a relay node for allocating by therelay node to user equipments for use by the user equipments undercontrol of the relay node; a transmitter configured to send to the relaynode the allocated radio resources for use by user equipments undercontrol of the relay node; a receiver configured to receive from therelay node a combination of a compound signal quality metric thataggregates channel quality experienced on links between the userequipments and the relay node using radio band resources from the grantallocated to corresponding user equipments, and an indication of thebuffer status of a relay node buffer which comprises individual buffersfor each of the plurality of user equipments, wherein the furtherindication of the buffer status comprises a buffer overload or a bufferunderload state determined individually for one or more of the pluralityof user equipments by prediction based on the compound signal qualitymetric; a processor configured to decide a new allocation of radioresources based at least in part on the received compound channelquality metric and on the indication of the buffer status; and thetransmitter is further to send to the relay node in a second instancethe new allocation of radio resources.
 48. A method comprising:allocating by an apparatus in a first instance radio resources to arelay node for allocating by the relay node to user equipments for useby the user equipments under control of the relay node; sending by theapparatus to the relay node a grant of radio band resources that areavailable for allocation to the user equipments; receiving by theapparatus from the relay node a combination of a compound signal qualitymetric that aggregates channel quality experienced on links between theuser equipments and the relay node using radio band resources from thegrant allocated to corresponding user equipments, and an indication ofthe buffer status of a relay node buffer which comprises individualbuffers for each of the plurality of user equipments, wherein thefurther indication of the buffer status comprises a buffer overload or abuffer underload state determined individually for one or more of theplurality of user equipments by prediction based on the compound signalquality metric; deciding by the apparatus a new allocation of radioresources based at least in part on the compound channel quality metricand on the indication of the buffer status; and allocating by theapparatus in a second instance the new allocation of radio resources tothe relay node.
 49. An apparatus comprising: a data processor configuredto allocate in a first instance radio resources to a relay node forallocating by the relay node to user equipments for use by the userequipments under control of the relay node; a transmitter configured tosend to the relay node the allocated radio resources for use by userequipments under control of the relay node; a receiver configured toreceive from the relay node a combination of a compound signal qualitymetric that aggregates channel quality experienced on links between theuser equipments and the relay node using radio band resources from thegrant allocated to corresponding user equipments, and an indication ofthe buffer status of a relay node buffer which comprises individualbuffers for each of the plurality of user equipments, wherein thefurther indication of the buffer status comprises a buffer overload or abuffer underload state determined individually for one or more of theplurality of user equipments by prediction based on the compound signalquality metric; a processor configured to decide a new allocation ofradio resources based at least in part on the received compound channelquality metric and on the indication of the buffer status; and thetransmitter is further to send to the relay node in a second instancethe new allocation of radio resources.